Sequences

Questions:
When a sequence is not either arithmetic or geometric, what is it considered? Is this when we apply the recursive definitions?

Mistakes:
Sometimes I get confused with some problems because I start thinking they're harder than what they actually are, and mess up something I know how to do. Also, there are times that simple mistakes in reducing, or negatives, change the answer.

Potential Quiz Problem:
The 20th and 40th terms of an arithmetic sequence are: 10 and -60.
A. Find the recursive definition of the quence.
B. Find the 76th term of the sequence.


Answers:
A: Tn= Tn-1 -3.5
Tn= T20 + (T20-1)(3.5)
T1= 10 + (66.5)
T1= 76.5
B: Tn= T1+ (n-1) d
Check first:
T40= 76.5 + (39)(-3.5)
T40= -60
So,
T76= 76.5 + (75)(-3.5)
T76= -186